A passive fiber optic star is a device used to distribute the optical information from one fiber optic source to several fiber optic receivers simultaneously, without an external source of power. The heart of the fiber optic star is its mixing element, a device by which the optical signal coming in from any of several input fibers is distributed more or less evenly among the output fibers. Characteristic features of mixing elements include a number of input and output ports, connection method, uniformity, insertion loss and excess loss. Insertion loss of the amount of attenuation experience between an input and output port. Excess loss of the amount of attenuation of the input signal before reaching the output ports. Such a system as described in U.S. Pat. No. 5,367,595 issued to Jennings et al on Nov. 22, 1994.
U.S. Pat. No. 5,402,512 issued to Jennings et al on Mar. 28, 1995 describes a seven fiber optic line star connection with a retainer that forms a mixing element into a predefined shape. The retainer constraints the mixing element on all sides. The mixing element in one embodiment is made from polymethylmethaacyalate, a material which shrinks approximate two percent when heated and cooled repeatedly. Because the mixing element is constrained on all sides, shrinkage occurs at the ends of the mixing element causing a gap to appear between the linear arrayed fibers and the mixing element. This gap greatly increases the optical insertion loss of the star.
This fiber optic coupling system includes an individual spring and terminal for each fiber plug into the star. As each fiber is plugged into the star, it is retained by a plastic lock. Because the space required for the "push, click, tug" locking mechanism of the system, the fibers must be spaced on 5 mm center lines. The incoming fibers are transitioned in each of three dimensions or directions down into a linear array. In order to minimize light loss, the fiber should not be bent on a radius smaller than 25 mm. Because of the large spacing between the fibers, each fiber must be transitioned many mm in each direction in order to lineup in the linear array without substantially reducing light loss. Accordingly, under this type of system configuration, the transition occurs over a length of 50 mm.
Further, under this fiber optical coupling system a complex assembly of parts is utilized to create channels which guide individual fibers into their appropriate positions in the linear array. The channel was created by assembling a convergent piece with a stop. A combination of two parts creates the channel which guides each fiber into position. The channels are not significantly tight however. The fibers when heated, lose some of their column strength, and tend to relax resulting in extra space in the channels. As a result, the ends of the fibers in the array tend to back away from the mixing element creating a gap and increasing the optical loss. Thus, a solution to the drawbacks of this type of system is needed.